MAYO CLINIC PROCEEDINGS

to report conclusions about its use with utmost accuracy. This is particularly important in light of the multiple studies that have touted the health benefits of coffee consumption. Although we applaud Liu et al for their important study, we are cautious about a potential disconnect between the data and their conclusions. Ultimately, it is evident that future investigations are merited to elucidate the relationship between coffee consumption and mortality. Michael G. Wagner Kapil G. Kapoor, MD Alan L. Wagner, MD Wagner Macula & Retina Center Virginia Beach, VA 1. Liu J, Sui X, Lavie CJ, et al. Association of coffee consumption with all-cause and cardiovascular disease mortality. Mayo Clin Proc. 2013;88(10):1066-1074. 2. Plowchalk DR, Rowland Yeo K. Prediction of drug clearance in a smoking population: modeling the impact of variable cigarette consumption on the induction of CYP1A2. Eur J Clin Pharmacol. 2012;68(6):951-960. 3. Parsons WD, Neims AH. Effect of smoking on caffeine clearance. Clin Pharmacol Ther. 1978;24(1):40-45. 4. Kenfield SA, Wei EK, Rosner BA, Glynn RJ, Stampfer MJ, Colditz GA. Burden of smoking on cause-specific mortality: application to the Nurses’ Health Study. Tob Control. 2010;19(3):248-254. 5. Freedman ND, Park Y, Abnet CC, Hollenbeck AR, Sinha R. Association of coffee drinking with total and cause-specific mortality [published correction appears in N Engl J Med. 2012;367(3):285]. N Engl J Med. 2012;366(20):1891-1904. http://dx.doi.org/10.1016/j.mayocp.2013.10.010

Importance of Sleep Disorders in Assessing the Association Between Coffee Consumption and All-Cause Mortality To the Editor: Liu et al1 have reported an interesting observational study in which they found a positive relationship between very high coffee consumption and all-cause mortality among men and among both men and women aged less than 55 years.1 Because the general finding for men appears to be attributable to the increased risk among those younger than 55 years, the authors concluded that “on the 1492

basis of these findings, it seems appropriate to suggest that younger people avoid heavy coffee consumption (ie, averaging >4 cups per day).” However, while this study’s findings are suggestive, it may be premature to make any clinical recommendations based on these results. This study has a number of strengths, including both a relatively large number of participants and adjustment for a broad array of potential confounders, but one key variable that was not included in the study was sleep disorders. Because one of the traditional uses of coffee is to compensate for feelings of sleepiness, it is reasonable to suppose that this may prove an important confounder, with higher consumption positively related to sleep disorders and the presence of sleep disorders positively related to all-cause mortality. Daytime sleepiness has been documented to be an independent risk factor for stroke and other vascular disease,2 and both insufficient and excessive sleep have been associated with an increased risk of all-cause mortality.3,4 Even more striking, the relationship between sleep disorders and all-cause mortality exhibits an age dependency similar to that reported by Liu et al. Lavie et al5 found that the excess mortality attributable to sleep apnea among men was limited to those younger than 50 years, and similar trends are also found in the relationship between long or short sleep and all-cause mortality.3 Of course, it is also possible that the causal pathway flows instead from excessive coffee consumption to insomnia and thence to an increased risk of mortality. Determining whether one or both of these scenarios explains the increased risk of mortality will require further research that takes sleep into account. It will also be important to measure sleep, coffee intake, and mortality at multiple time points throughout the study in order to establish the temporal sequence between sleep and coffee consumption and to account for changes in these variables over time.

The study by Liu et al1 is an important contribution toward a better understanding of the relationship between coffee intake and all-cause mortality, but the state of the science may be too young at this time to enable clinicians or public health authorities to provide specific advice to patients. Alan J. Card, PhD, MPH, CPH, CPHQ Evidence-Based Health Solutions, LLC Notre Dame, IN

1. Liu J, Sui X, Lavie CJ, et al. Association of coffee consumption with all-cause and cardiovascular disease mortality. Mayo Clin Proc. 2013;88(10):1066-1074. 2. Boden-Albala B, Roberts ET, Bazil C, et al. Daytime sleepiness and risk of stroke and vascular disease: findings from the Northern Manhattan Study (NOMAS). Circ Cardiovasc Qual Outcomes. 2012; 5(4):500-507. 3. Hublin C, Partinen M, Koskenvuo M, Kaprio J. Sleep and mortality: a population-based 22-year followup study. Sleep. 2007;30(10):1245-1253. 4. Gallicchio L, Kalesan B. Sleep duration and mortality: a systematic review and meta-analysis. J Sleep Res. 2009;18(2):148-158. 5. Lavie P, Lavie L, Herer P. All-cause mortality in males with sleep apnoea syndrome: declining mortality rates with age. Eur Respir J. 2005;25(3):514-520. http://dx.doi.org/10.1016/j.mayocp.2013.10.005

Heavy Coffee Drinking and Age-Dependent All-Cause Mortality To the Editor: The study by Liu et al1 reported in the October 2013 issue of Mayo Clinic Proceedings associated heavy coffee drinking with increased all-cause mortality in people younger than 55 years. A previous study,2 however, associated heavy coffee drinking with a decrease in all-cause mortality. Both studies included large populations with long follow-up and made adjustments for smoking, alcohol consumption, and other potential health effectors. In both studies, a similar effect was attributed to either caffeine or caffeine-free drinks.1,2 Thus, the agent searched for was not the caffeine. Coffee, especially when brewed, contains many antioxidants such as Mayo Clin Proc.

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December 2013;88(12):1491-1494 www.mayoclinicproceedings.org

Importance of sleep disorders in assessing the association between coffee consumption and all-cause mortality.

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